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An iterative approach to mixed equilibrium problems and fixed points problems

Fixed Point Theory and Applications20132013:183

https://doi.org/10.1186/1687-1812-2013-183

  • Received: 25 February 2013
  • Accepted: 28 June 2013
  • Published:

Abstract

In the present paper, an iterative algorithm for solving mixed equilibrium problems and fixed points problems has been constructed. It is shown that under some mild conditions, the sequence generated by the presented algorithm converges strongly to the common solution of mixed equilibrium problems and fixed points problems. As an application, we can find the minimum norm element without involving projection.

MSC:47J05, 47J25, 47H09.

Keywords

  • mixed equilibrium problem
  • fixed point problem
  • minimization problem
  • strictly pseudo-contractive mapping

1 Introduction

Let H be a real Hilbert space with the inner product , and the norm , respectively. Let C be a nonempty closed convex subset of H. For a nonlinear mapping A : C H and a bifunction F : C × C R , the mixed equilibrium problem is to find z C such that
F ( z , y ) + A z , y z 0 , y C .
(1.1)
The solution set of (1.1) is denoted by MEP. If A = 0 , then (1.1) reduces to the following equilibrium problem of finding z C such that
F ( z , y ) 0 , y C .
(1.2)
The solution set of (1.2) is denoted by EP. If F = 0 , then (1.1) reduces to the variational inequality problem of finding z C such that
A z , y z 0 , y C .
(1.3)

The solution set of (1.3) is denoted by VI. Problem (1.1) is very general in the sense that it includes, as special cases, optimization problems, variational inequalities, minimax problems, Nash equilibrium problem in noncooperative games and others. See, e.g., [122].

For solving mixed equilibrium problem (1.1), Moudafi [9] introduced an iterative algorithm and proved a weak convergence theorem. Further, Takahashi and Takahashi [15] introduced the following iterative algorithm for finding an element of F ( S ) MEP :
{ F ( z n , y ) + A x n , y z n + 1 λ n y z n , z n x n 0 , y C , x n + 1 = β n x n + S ( α n u + ( 1 β n ) z n )
(1.4)

for all n 0 , where S : C C is a nonexpansive mapping. They proved that the sequence { x n } generated by (1.4) converges strongly to z = Proj F ( S ) MEP ( u ) .

Recently, Yao and Shahzad [19] gave the following iteration process for nonexpansive mappings with perturbation: x 1 C and
x n + 1 = ( 1 β n ) x n + β n Proj C ( α n u n + ( 1 α n ) T x n ) , n 0 ,

where { α n } and { β n } are sequences in [ 0 , 1 ] , and the sequence { u n } in H is a small perturbation for the n-step iteration satisfying u n 0 as n . In fact, there are perturbations always occurring in the iterative processes because the manipulations are inaccurate.

Using the ideas in [19], Chuang et al. [4] introduced the following iteration process for finding a common element of the set of solutions of the equilibrium problem and the set of fixed points for a quasi-nonexpansive mapping with perturbation: q 1 H and
{ x n C  such that  F ( x n , y ) + 1 λ n y x n , x n q n 0 , y C , q n + 1 = α n u n + ( 1 α n ) ( β n x n + ( 1 β n ) S x n )

for all n 0 . They showed that the sequence { q n } converges strongly to Proj F ( S ) EP .

Motivated and inspired by the above works, in the present paper, we construct an iterative algorithm for solving mixed equilibrium problems and fixed points problems. It is shown that under some mild conditions the sequence { x n } generated by the presented algorithm converges strongly to the common solution of mixed equilibrium problems and fixed points problems. As an application, we can find the minimum norm element without involving projection.

2 Preliminaries

Let C be a nonempty closed convex subset of a real Hilbert space H. Recall that a mapping A : C H is called α-inverse-strongly monotone if there exists a positive real number α > 0 such that
A x A y , x y α A x A y 2 , x , y C .
It is clear that any α-inverse-strongly monotone mapping is monotone and 1 α -Lipschitz continuous. A mapping S : C C is said to be nonexpansive if S x S y x y for all x , y C . And a mapping S : C C is said to be strictly pseudo-contractive if there exists a constant 0 κ < 1 such that
S x S y 2 x y 2 + κ ( I S ) x ( I S ) y 2 , x , y C .

For such a case, we also say that S is a κ-strictly pseudo-contractive mapping.

Throughout this paper, we assume that a bifunction F : C × C R satisfies the following conditions:
  1. (H1)

    F ( x , x ) = 0 for all x C ;

     
  2. (H2)

    F is monotone, i.e., F ( x , y ) + F ( y , x ) 0 for all x , y C ;

     
  3. (H3)

    for each x , y , z C , lim t 0 F ( t z + ( 1 t ) x , y ) F ( x , y ) ;

     
  4. (H4)

    for each x C , y F ( x , y ) is convex and lower semicontinuous.

     

We need the following lemmas for proving our main results.

Lemma 2.1 [7]

Let C be a nonempty closed convex subset of a real Hilbert space H. Let F : C × C R be a bifunction which satisfies conditions (H1)-(H4). Let r > 0 and x H . Then there exists z C such that
F ( z , y ) + 1 r y z , z x 0 , y C .
Further, if T r ( x ) = { z C : F ( z , y ) + 1 r y z , z x 0 , y C } , then we have
  1. (i)

    T r is single-valued and T r is firmly nonexpansive, i.e., for any x , y H , T r x T r y 2 T r x T r y , x y ;

     
  2. (ii)

    EP is closed and convex and EP = F ( T r ) .

     

Lemma 2.2 [19]

Let C, H, F and T r x be as in Lemma  2.1. Then we have
T s x T t x 2 s t s T s x T t x , T s x x

for all s , t > 0 and x H .

Lemma 2.3 [19]

Let C be a nonempty closed convex subset of a real Hilbert space H. Let the mapping A : C H be α-inverse strongly monotone and r > 0 be a constant. Then we have
( I r A ) x ( I r A ) y 2 x y 2 + r ( r 2 α ) A x A y 2 , x , y C .

In particular, if 0 r 2 α , then I r A is nonexpansive.

Lemma 2.4 [23]

Let { x n } and { y n } be bounded sequences in a Banach space X and let { β n } be a sequence in [ 0 , 1 ] with 0 < lim inf n β n lim sup n β n < 1 . Suppose that x n + 1 = ( 1 β n ) y n + β n x n for all n 0 and lim sup n ( y n + 1 y n x n + 1 x n ) 0 . Then lim n y n x n = 0 .

Lemma 2.5 [24]

Let C be a nonempty closed convex subset of a real Hilbert space H. Let S : C C be a λ-strict pseudo-contraction. Then we have
  1. (i)

    F ( S ) = { x : S x = x } is closed convex;

     
  2. (ii)

    κ I + ( 1 κ ) S for κ [ λ , 1 ) is nonexpansive.

     

Lemma 2.6 [25]

Let C be a nonempty closed and convex of a real Hilbert space H. Let S : C C be a κ-strictly pseudo-contractive mapping. Then I S is demi-closed at 0, i.e., if x n x C and x n S x n 0 , then x = S x .

Lemma 2.7 [16]

Assume that { a n } is a sequence of nonnegative real numbers such that
a n + 1 ( 1 γ n ) a n + δ n γ n ,
where { γ n } is a sequence in ( 0 , 1 ) and { δ n } is a sequence such that
  1. (1)

    n = 1 γ n = ;

     
  2. (2)

    lim sup n δ n 0 or n = 1 | δ n γ n | < .

     

Then lim n a n = 0 .

3 Main results

In this section, we prove our main results.

Theorem 3.1 Let C be a nonempty closed convex subset of a real Hilbert space H and let F : C × C R be a bifunction satisfying conditions (H1)-(H4). Let A : C H be an α-inverse-strongly monotone mapping and let S : C C be a κ-strictly pseudo-contractive mapping. Suppose that F ( S ) MEP . Let x 0 C , { z n } and { x n } be sequences in C generated by
{ F ( z n , y ) + A x n , y z n + 1 λ n y z n , z n ( α n u n + ( 1 α n ) x n ) 0 , y C , x n + 1 = β n x n + ( 1 β n ) γ z n + ( 1 β n ) ( 1 γ ) S z n ,
(3.1)
for all n 0 , where { λ n } ( 0 , 2 α ) , { α n } ( 0 , 1 ) and { β n } ( 0 , 1 ) satisfy
  1. (r1)

    lim n u n = u for some u H ;

     
  2. (r2)

    lim n α n = 0 and n = 1 α n = ;

     
  3. (r3)

    0 < c β n d < 1 and γ [ κ , 1 ) ;

     
  4. (r4)

    a ( 1 α n ) λ n b ( 1 α n ) , where [ a , b ] ( 0 , 2 α ) and lim n ( λ n + 1 λ n ) = 0 .

     

Then { x n } generated by (3.1) converges strongly to Proj F ( S ) MEP ( u ) .

Proof Note that z n can be rewritten as z n = T λ n ( α n u n + ( 1 α n ) x n λ n A x n ) for each n. Take z F ( S ) MEP . It is obvious that z = T λ n ( z λ n A z ) = T λ n ( α n z + ( 1 α n ) ( z λ n A z 1 α n ) ) for all n 0 . By using the nonexpansivity of T λ n and the convexity of , we derive
z n z 2 = T λ n ( α n u n + ( 1 α n ) x n λ n A x n ) T λ n ( z λ n A z ) 2 = T λ n ( α n u n + ( 1 α n ) ( x n λ n A x n 1 α n ) ) T λ n ( α n z + ( 1 α n ) ( z λ n A z 1 α n ) ) 2 ( α n u n + ( 1 α n ) ( x n λ n A x n 1 α n ) ) ( α n z + ( 1 α n ) ( z λ n A z 1 α n ) ) 2 = ( 1 α n ) ( ( x n λ n A x n 1 α n ) ( z λ n A z 1 α n ) ) + α n ( u n z ) 2 ( 1 α n ) ( x n λ n A x n 1 α n ) ( z λ n A z 1 α n ) 2 + α n u n z 2 .
Since A is α-inverse strongly monotone, we know from Lemma 2.3 that
( x n λ n A x n 1 α n ) ( z λ n A z 1 α n ) 2 x n z 2 + λ n ( λ n 2 ( 1 α n ) α ) ( 1 α n ) 2 A x n A z 2 .
It follows that
z n z 2 ( 1 α n ) ( x n z 2 + λ n ( λ n 2 ( 1 α n ) α ) ( 1 α n ) 2 A x n A z 2 ) + α n u n z 2 ( 1 α n ) x n z 2 + α n u n z 2 .
(3.2)
So, we have
x n + 1 z 2 = β n ( x n z ) + ( 1 β n ) ( ( γ I + ( 1 γ ) S ) z n z ) 2 β n x n z 2 + ( 1 β n ) z n z 2 β n x n z 2 + ( 1 β n ) ( ( 1 α n ) x n z 2 + α n u n z 2 ) = [ 1 ( 1 β n ) α n ] x n z 2 + ( 1 β n ) α n u n z 2 max { x n z 2 , u n z 2 } .

Since lim n u n = u , { u n } is bounded. Therefore, by induction, we deduce that { x n } is bounded. Hence, { A x n } , { z n } and { S z n } are also bounded.

Putting y n = α n u n + ( 1 α n ) x n λ n A x n for all n, we have
z n + 1 z n = T λ n + 1 y n + 1 T λ n + 1 y n + T λ n + 1 y n T λ n y n .
It follows that
z n + 1 z n T λ n + 1 y n + 1 T λ n + 1 y n + T λ n + 1 y n T λ n y n y n + 1 y n + T λ n + 1 y n T λ n y n .
(3.3)
From Lemma 2.3, we know that I λ A is nonexpansive for all λ ( 0 , 2 α ) . Thus, we have I λ n + 1 1 α n + 1 A is nonexpansive for all n due to the fact that λ n + 1 1 α n + 1 ( 0 , 2 α ) . Then we get
y n + 1 y n = α n + 1 u n + 1 + ( 1 α n + 1 ) x n + 1 λ n + 1 A x n + 1 ( α n u n + ( 1 α n ) x n λ n A x n ) ( 1 α n + 1 ) ( x n + 1 λ n + 1 1 α n + 1 A x n + 1 ) ( 1 α n ) ( x n λ n 1 α n A x n ) + α n + 1 u n + 1 + α n u n ( 1 α n + 1 ) ( I λ n + 1 1 α n + 1 A ) x n + 1 ( I λ n + 1 1 α n + 1 A ) x n + ( 1 α n + 1 ) ( x n λ n + 1 1 α n + 1 A x n ) ( 1 α n ) ( x n λ n 1 α n A x n ) + α n + 1 u n + 1 + α n u n x n + 1 x n + | α n + 1 α n | x n + | λ n + 1 λ n | A x n + α n + 1 u n + 1 + α n u n .
(3.4)
By Lemma 2.2, we have
T λ n + 1 y n T λ n y n | λ n + 1 λ n | λ n + 1 T λ n + 1 y n y n .
(3.5)
From (3.3)-(3.5), we obtain
z n + 1 z n x n + 1 x n + | α n + 1 α n | x n + | λ n + 1 λ n | A x n + | λ n + 1 λ n | λ n + 1 T λ n + 1 y n y n + α n + 1 u n + 1 + α n u n .
Then
( γ I + ( 1 γ ) S ) z n + 1 ( γ I + ( 1 γ ) S ) z n z n + 1 z n x n + 1 x n + | α n + 1 α n | x n + | λ n + 1 λ n | A x n + | λ n + 1 λ n | λ n + 1 T λ n + 1 y n y n + α n + 1 u n + 1 + α n u n .
Therefore,
( γ I + ( 1 γ ) S ) z n + 1 ( γ I + ( 1 γ ) S ) z n x n + 1 x n | α n + 1 α n | x n + | λ n + 1 λ n | A x n + α n + 1 u n + 1 + α n u n + | λ n + 1 λ n | λ n + 1 T λ n + 1 y n y n .
Since α n 0 , λ n + 1 λ n 0 and lim inf n λ n > 0 , we obtain
lim sup n ( ( γ I + ( 1 γ ) S ) z n + 1 ( γ I + ( 1 γ ) S ) z n x n + 1 x n ) 0 .
This together with Lemma 2.4 implies that
lim n ( γ I + ( 1 γ ) S ) z n x n = 0 .
(3.6)
Consequently, we obtain
lim n x n + 1 x n = lim n ( 1 β n ) ( γ I + ( 1 γ ) S ) z n x n = 0 .
From (3.1) and (3.2), we have
x n + 1 z 2 ( 1 β n ) ( γ I + ( 1 γ ) S ) T λ n ( α n u n + ( 1 α n ) x n λ n A x n ) z 2 + β n x n z 2 ( 1 β n ) { ( 1 α n ) ( x n z 2 + λ n ( 1 α n ) 2 ( λ n 2 ( 1 α n ) α ) A x n A z 2 ) + α n u n z 2 } + β n x n z 2 = ( 1 ( 1 β n ) α n ) x n z 2 + ( 1 β n ) λ n 1 α n ( λ n 2 ( 1 α n ) α ) A x n A z 2 + ( 1 β n ) α n u n z 2 x n z 2 + ( 1 β n ) λ n 1 α n ( λ n 2 ( 1 α n ) α ) A x n A z 2 + ( 1 β n ) α n u n z 2 .
Then we obtain
( 1 β n ) λ n 1 α n ( 2 ( 1 α n ) α λ n ) A x n A z 2 x n z 2 x n + 1 z 2 + ( 1 β n ) α n u n z 2 ( x n z x n + 1 z ) x n + 1 x n + ( 1 β n ) α n u n z 2 .
Since lim n α n = 0 , lim n x n + 1 x n = 0 and lim inf n ( 1 β n ) λ n 1 α n ( 2 ( 1 α n ) α λ n ) > 0 , we have
lim n A x n A z = 0 .
(3.7)
Next, we show x n z n = x n T λ n y n 0 . By using the firm nonexpansivity of T λ n , we have
T λ n y n z 2 = T λ n y n T λ n ( z λ n A z ) 2 y n ( z λ n A z ) , T λ n y n z = 1 2 ( y n ( z λ n A z ) 2 + T λ n y n z 2 α n u n + ( 1 α n ) x n λ n ( A x n λ n A z ) T λ n y n 2 ) .
We note that
y n ( z λ n A z ) 2 ( 1 α n ) x n z 2 + α n u n z 2 .
Thus,
T λ n y n z 2 1 2 ( ( 1 α n ) x n z 2 + α n u n z 2 + T λ n y n z 2 α n u n + ( 1 α n ) x n T λ n y n λ n ( A x n λ n A z ) 2 ) .
That is,
T λ n y n z 2 ( 1 α n ) x n z 2 + α n u n z 2 α n u n + ( 1 α n ) x n T λ n y n λ n ( A x n λ n A z ) 2 = ( 1 α n ) x n z 2 + α n u n z 2 α n u n + ( 1 α n ) x n T λ n y n 2 + 2 λ n α n u n + ( 1 α n ) x n T λ n y n , A x n A z λ n 2 A x n A z 2 ( 1 α n ) x n z 2 + α n u n z 2 α n u n + ( 1 α n ) x n T λ n y n 2 + 2 λ n α n u n + ( 1 α n ) x n T λ n y n A x n A z .
It follows that
x n + 1 z 2 β n x n z 2 + ( 1 β n ) ( 1 α n ) x n z 2 + ( 1 β n ) α n u n z 2 ( 1 β n ) α n u n + ( 1 α n ) x n T λ n y n 2 + 2 λ n ( 1 β n ) α n u n + ( 1 α n ) x n T λ n y n A x n A z = ( 1 ( 1 β n ) α n ) x n z 2 + ( 1 β n ) α n u n z 2 ( 1 β n ) α n u n + ( 1 α n ) x n T λ n y n 2 + 2 λ n ( 1 β n ) α n u n + ( 1 α n ) x n T λ n y n A x n A z .
Hence,
( 1 β n ) α n u n + ( 1 α n ) x n T λ n y n 2 x n z 2 x n + 1 z 2 ( 1 β n ) α n x n z 2 + ( 1 β n ) α n u n z 2 + 2 λ n ( 1 β n ) α n u n + ( 1 α n ) x n T λ n y n A x n A z ( x n z + x n + 1 z ) x n + 1 x n + ( 1 β n ) α n u n z 2 + 2 λ n ( 1 β n ) α n u n + ( 1 α n ) x n T λ n y n A x n A z .
Since lim sup n β n < 1 , x n + 1 x n 0 , α n 0 and A x n A z 0 , we deduce
lim n α n u n + ( 1 α n ) x n T λ n y n = 0 .
This implies that
lim n x n z n = x n T λ n y n = 0 .
(3.8)

Put x ˜ = Proj F ( S ) MEP ( u ) . We will finally show that x n x ˜ .

Setting v n = x n λ n 1 α n ( A x n A x ˜ ) for all n. Taking z = x ˜ in (3.7) to get A x n A x ˜ 0 . First, we prove lim sup n u x ˜ , v n x ˜ 0 . We take a subsequence { v n i } of { v n } such that
lim sup n u x ˜ , v n x ˜ = lim i u x ˜ , v n i x ˜ .
It is clear that { v n i } is bounded due to the boundedness of { x n } and A x n A x ˜ 0 . Then there exists a subsequence { v n i j } of { v n i } which converges weakly to some point w C . Hence, { x n i j } also converges weakly to w. At the same time, from (3.6) and (3.8), we have
lim j x n i j ( γ I + ( 1 γ ) S ) x n i j = 0 .
(3.9)

By the demi-closedness principle (see Lemma 2.6) and (3.9), we deduce w F ( S ) .

Further, we show that w is also in MEP. From (3.1), we have
F ( z n , y ) + A x n , y z n + 1 λ n y z n , z n ( α n u n + ( 1 α n ) x n ) 0 .
From (H2), we have
A x n , y z n + 1 λ n y z n , z n ( α n u n + ( 1 α n ) x n ) F ( y , z n ) .
(3.10)
Put x t = t y + ( 1 t ) w for all t ( 0 , 1 λ 2 α ) and y C . Then we have x t C . So, from (3.10), we have
x t z n , A x t x t z n , A x t x t z n , A x n 1 λ n x t z n , z n ( α n u n + ( 1 α n ) x n ) + F ( x t , z n ) = x t z n , A x t A z n + x t z n , A z n A x n 1 λ n x t z n , z n ( α n u n + ( 1 α n ) x n ) + F ( x t , z n ) .
Since z n x n 0 , we have A z n A x n 0 . Further, from monotonicity of A, we have x t z n , A x t A z n 0 . So, from (H4), we have
x t w , A x t F ( x t , w ) , as  n .
(3.11)
From (H1), (H4) and (3.11), we also have
0 = F ( x t , x t ) t F ( x t , y ) + ( 1 t ) F ( x t , w ) t F ( x t , y ) + ( 1 t ) x t w , A x t = t F ( x t , y ) + ( 1 t ) t y w , A x t
and hence
0 F ( x t , y ) + ( 1 t ) y w , A x t .
Letting t 0 , we have, for each y C ,
0 F ( w , y ) + y w , A w .
This implies w MEP . Hence, we have w F ( S ) MEP . This implies that
lim sup n u x ˜ , v n x ˜ = lim j u x ˜ , v n i j x ˜ = u x ˜ , w x ˜ .
Note that x ˜ = Proj F ( S ) MEP ( u ) . Then u x ˜ , w x ˜ 0 , w F ( S ) MEP . Therefore,
lim sup n u x ˜ , v n x ˜ 0 .
Since u n u , we have
lim sup n u n x ˜ , v n x ˜ 0 .
From (3.1), we have
x n + 1 x ˜ 2 β n x n x ˜ 2 + ( 1 β n ) ( γ I + ( 1 γ ) S ) T λ n y n x ˜ 2 β n x n x ˜ 2 + ( 1 β n ) T λ n y n x ˜ 2 = β n x n x ˜ 2 + ( 1 β n ) T λ n y n T λ n ( x ˜ λ n A x ˜ ) 2 β n x n x ˜ 2 + ( 1 β n ) y n ( x ˜ λ n A x ˜ ) 2 = β n x n x ˜ 2 + ( 1 β n ) α n u n + ( 1 α n ) x n λ n A x n ( x ˜ λ n A x ˜ ) 2 = ( 1 β n ) ( 1 α n ) ( ( x n λ n 1 α n A x n ) ( x ˜ λ n 1 α n A x ˜ ) ) + α n ( u n x ˜ ) 2 + β n x n x ˜ 2 = ( 1 β n ) ( ( 1 α n ) 2 ( x n λ n 1 α n A x n ) ( x ˜ λ n 1 α n A x ˜ ) 2 + 2 α n ( 1 α n ) u n x ˜ , ( x n λ n 1 α n A x n ) ( x ˜ λ n 1 α n A x ˜ ) + α n 2 u n x ˜ 2 ) + β n x n x ˜ 2 β n x n x ˜ 2 + ( 1 β n ) ( ( 1 α n ) 2 x n x ˜ 2 + 2 α n ( 1 α n ) u n x ˜ , x n λ n 1 α n ( A x n A x ˜ ) x ˜ + α n 2 u n x ˜ 2 ) ( 1 ( 1 β n ) α n ) x n x ˜ 2 + ( 1 β n ) α n { 2 ( 1 α n ) u n x ˜ , v n x ˜ + α n u n x ˜ 2 } .

It is clear that n = 1 ( 1 β n ) α n = and lim sup n ( 2 ( 1 α n ) u n x ˜ , v n x ˜ + α n u n x ˜ 2 ) 0 . We can therefore apply Lemma 2.7 to conclude that x n x ˜ . This completes the proof. □

Corollary 3.2 Let C be a nonempty closed convex subset of a real Hilbert space H and let F : C × C R be a bifunction satisfying conditions (H1)-(H4). Let A : C H be an α-inverse-strongly monotone mapping and let S : C C be a nonexpansive mapping. Suppose that F ( S ) MEP . Let x 0 C , { z n } and { x n } be sequences in C generated by
{ F ( z n , y ) + A x n , y z n + 1 λ n y z n , z n ( α n u n + ( 1 α n ) x n ) 0 , y C , x n + 1 = β n x n + ( 1 β n ) γ z n + ( 1 β n ) ( 1 γ ) S z n
(3.12)
for all n 0 , where { λ n } ( 0 , 2 α ) , { α n } ( 0 , 1 ) and { β n } ( 0 , 1 ) satisfy
  1. (r1)

    lim n u n = u for some u H ;

     
  2. (r2)

    lim n α n = 0 and n = 1 α n = ;

     
  3. (r3)

    0 < c β n d < 1 and γ ( 0 , 1 ) ;

     
  4. (r4)

    a ( 1 α n ) λ n b ( 1 α n ) , where [ a , b ] ( 0 , 2 α ) and lim n ( λ n + 1 λ n ) = 0 .

     

Then { x n } generated by (3.12) converges strongly to Proj F ( S ) MEP ( u ) .

Corollary 3.3 Let C be a nonempty closed convex subset of a real Hilbert space H and let F : C × C R be a bifunction satisfying conditions (H1)-(H4). Let S : C C be a κ-strictly pseudo-contractive mapping. Suppose that F ( S ) EP . Let x 0 C , { z n } and { x n } be sequences in C generated by
{ F ( z n , y ) + 1 λ n y z n , z n ( α n u n + ( 1 α n ) x n ) 0 , y C , x n + 1 = β n x n + ( 1 β n ) γ z n + ( 1 β n ) ( 1 γ ) S z n
(3.13)
for all n 0 , where { λ n } ( 0 , 1 ) , { α n } ( 0 , 1 ) and { β n } ( 0 , 1 ) satisfy
  1. (r1)

    lim n u n = u for some u H ;

     
  2. (r2)

    lim n α n = 0 and n = 1 α n = ;

     
  3. (r3)

    0 < c β n d < 1 and γ [ κ , 1 ) ;

     
  4. (r4)

    a ( 1 α n ) λ n b ( 1 α n ) , where [ a , b ] ( 0 , 1 ) and lim n ( λ n + 1 λ n ) = 0 .

     

Then { x n } generated by (3.13) converges strongly to Proj F ( S ) EP ( u ) .

Corollary 3.4 Let C be a nonempty closed convex subset of a real Hilbert space H and let F : C × C R be a bifunction satisfying conditions (H1)-(H4). Let S : C C be a nonexpansive mapping. Suppose that F ( S ) EP . Let x 0 C , { z n } and { x n } be sequences in C generated by
{ F ( z n , y ) + 1 λ n y z n , z n ( α n u n + ( 1 α n ) x n ) 0 , y C , x n + 1 = β n x n + ( 1 β n ) γ z n + ( 1 β n ) ( 1 γ ) S z n
(3.14)
for all n 0 , where { λ n } ( 0 , 1 ) , { α n } ( 0 , 1 ) and { β n } ( 0 , 1 ) satisfy
  1. (r1)

    lim n u n = u for some u H ;

     
  2. (r2)

    lim n α n = 0 and n = 1 α n = ;

     
  3. (r3)

    0 < c β n d < 1 and γ ( 0 , 1 ) ;

     
  4. (r4)

    a ( 1 α n ) λ n b ( 1 α n ) , where [ a , b ] ( 0 , 1 ) and lim n ( λ n + 1 λ n ) = 0 .

     

Then { x n } generated by (3.14) converges strongly to Proj F ( S ) EP ( u ) .

Corollary 3.5 Let C be a nonempty closed convex subset of a real Hilbert space H and let F : C × C R be a bifunction satisfying conditions (H1)-(H4). Let A : C H be an α-inverse-strongly monotone mapping and let S : C C be a κ-strictly pseudo-contractive mapping. Suppose that F ( S ) MEP . Let x 0 C , { z n } and { x n } be sequences in C generated by
{ F ( z n , y ) + A x n , y z n + 1 λ n y z n , z n ( 1 α n ) x n 0 , y C , x n + 1 = β n x n + ( 1 β n ) γ z n + ( 1 β n ) ( 1 γ ) S z n
(3.15)
for all n 0 , where { λ n } ( 0 , 2 α ) , { α n } ( 0 , 1 ) and { β n } ( 0 , 1 ) satisfy
  1. (r2)

    lim n α n = 0 and n = 1 α n = ;

     
  2. (r3)

    0 < c β n d < 1 and γ [ κ , 1 ) ;

     
  3. (r4)

    a ( 1 α n ) λ n b ( 1 α n ) , where [ a , b ] ( 0 , 2 α ) and lim n ( λ n + 1 λ n ) = 0 .

     

Then { x n } generated by (3.15) converges strongly to Proj F ( S ) MEP ( 0 ) , which is the minimum norm element in F ( S ) MEP .

Corollary 3.6 Let C be a nonempty closed convex subset of a real Hilbert space H and let F : C × C R be a bifunction satisfying conditions (H1)-(H4). Let S : C C be a κ-strictly pseudo-contractive mapping. Suppose that F ( S ) EP . Let x 0 C , { z n } and { x n } be sequences in C generated by
{ F ( z n , y ) + 1 λ n y z n , z n ( 1 α n ) x n 0 , y C , x n + 1 = β n x n + ( 1 β n ) γ z n + ( 1 β n ) ( 1 γ ) S z n
(3.16)
for all n 0 , where { λ n } ( 0 , 1 ) , { α n } ( 0 , 1 ) and { β n } ( 0 , 1 ) satisfy
  1. (r2)

    lim n α n = 0 and n = 1 α n = ;

     
  2. (r3)

    0 < c β n d < 1 and γ [ κ , 1 ) ;

     
  3. (r4)

    a ( 1 α n ) λ n b ( 1 α n ) , where [ a , b ] ( 0 , 1 ) and lim n ( λ n + 1 λ n ) = 0 .

     

Then { x n } generated by (3.16) converges strongly to Proj F ( S ) EP ( 0 ) , which is the minimum norm element in F ( S ) EP .

Corollary 3.7 Let C be a nonempty closed convex subset of a real Hilbert space H and let F : C × C R be a bifunction satisfying conditions (H1)-(H4). Let A : C H be an α-inverse-strongly monotone mapping. Suppose that MEP . Let x 0 C , { z n } and { x n } be sequences in C generated by
{ F ( z n , y ) + A x n , y z n + 1 λ n y z n , z n ( 1 α n ) x n 0 , y C , x n + 1 = β n x n + ( 1 β n ) z n
(3.17)
for all n 0 , where { λ n } ( 0 , 2 α ) , { α n } ( 0 , 1 ) and { β n } ( 0 , 1 ) satisfy
  1. (r2)

    lim n α n = 0 and n = 1 α n = ;

     
  2. (r3)

    0 < c β n d < 1 ;

     
  3. (r4)

    a ( 1 α n ) λ n b ( 1 α n ) , where [ a , b ] ( 0 , 2 α ) and lim n ( λ n + 1 λ n ) = 0 .

     

Then { x n } generated by (3.17) converges strongly to Proj MEP ( 0 ) , which is the minimum norm element in MEP.

Corollary 3.8 Let C be a nonempty closed convex subset of a real Hilbert space H and let F : C × C R be a bifunction satisfying conditions (H1)-(H4). Suppose EP . Let x 0 C , { z n } and { x n } be sequences in C generated by
{ F ( z n , y ) + 1 λ n y z n , z n ( 1 α n ) x n 0 , y C , x n + 1 = β n x n + ( 1 β n ) z n
(3.18)
for all n 0 , where { λ n } ( 0 , 1 ) , { α n } ( 0 , 1 ) and { β n } ( 0 , 1 ) satisfy
  1. (r2)

    lim n α n = 0 and n = 1 α n = ;

     
  2. (r3)

    0 < c β n d < 1 ;

     
  3. (r4)

    a ( 1 α n ) λ n b ( 1 α n ) , where [ a , b ] ( 0 , 1 ) and lim n ( λ n + 1 λ n ) = 0 .

     

Then { x n } generated by (3.18) converges strongly to Proj EP ( 0 ) , which is the minimum norm element in EP.

Declarations

Authors’ Affiliations

(1)
Department of Mathematics, Tianjin Polytechnic University, Tianjin, 300387, China
(2)
Department of Information Management, Cheng Shiu University, Kaohsiung, 833, Taiwan
(3)
Department of Mathematics and the RINS, Gyeongsang National University, Jinju, 660-701, Korea

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© Yao et al.; licensee Springer 2013

This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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